1. Field of the Invention
The present invention relates to a noise-shield sheet and a liquid crystal display device using such a noise-shield sheet. More particularly, the present invention relates to a noise-shield sheet which can shield without any complicated wiring and a liquid crystal display device using such a noise-shield sheet.
2. Description of the Prior Art
The background art of the present invention provides a liquid crystal display device shown in FIG. 18, for example.
Such a liquid crystal display device is small sufficient to be a display module in pagers and cameras. The liquid crystal display device comprises a metallic frame 10 in which a liquid crystal display panel 12, a reflector 14 and a circuit board 16 are mounted.
The circuit board 16 includes a lamp 18 which radiates a light from the side edge of the liquid crystal display panel 12. The light is then reflected by the reflector 14 from the backside of the liquid crystal display panel 12 to provide a back light.
The bottom surface of the liquid crystal display panel 12 and the top surface of the circuit board 16 respectively include connecting terminals 20 and 22 which are separated from one another along one longitudinal side of the respective members. These connecting terminals 20 and 22 are connected to one another through an electrically conductive rubber 24 between the liquid crystal display panel 12 and the circuit board 16.
In such a case, it is required to prevent such elements as the mother board from adverse effects of noise from the circuit board 16, since the circuit board 16 is connected to the mother board or the like.
To meet such a requirement, for example, the circuit board 16 may be multi-layered and the shield layers are formed on the top and bottom surfaces of each outermost layer of the board. The outermost shield layers are connected to each other by means of holes.
Alternatively, copper foils may be applied to the top and bottom surfaces of the circuit board and connected to each other through soldering or single-sided boards each having a whole pattern may be applied on the top and bottom surfaces of the circuit board and connected to each other through conductors.
When the circuit board 16 is multi-layered and if the wiring on the multi-layered board is complicated, the shield layers cannot be formed on the outermost layers of the multi-layered board.
Such a multi-layered board raises another problem in that it is substantially expensive.
When the copper foils are applied to the circuit board and connected to each other through the soldering as described, the copper foils should be formed with holes used to avoid various electronic parts and connection terminals on the circuit board 16. However, it is difficult to accurately position and form these holes. If the holes are formed slightly out of their proper positions, the copper foil portions will be exposed in the holes. This tends to create a short-circuiting between the electronic parts and the copper foils.
When the single-sided boards are applied to the top and bottom surfaces of the circuit board 16 and connected to each other through conductors or when the copper foils are connected to each other through the soldering, it raises a further problem in that tedious connecting or soldering operation is required.